Differentials are known in the automotive industry as devices that split engine torque two ways, allowing each output to spin at a different speed. Generally, differentials have three primary tasks: to aim the engine power at the wheels; to act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before transmission to the wheels; and to transmit the power to the wheels while allowing them to rotate at different speeds.
A typical mechanical differential contains a housing (or carrier), two side gears, and several pinion gears. A rotating driveshaft of the vehicle engages a ring gear, which is mounted onto the differential housing. The driveshaft drives the ring gear, which in turn rotates the differential housing. Pinion shafts attach the pinion gears to the housing so that, as the housing rotates, the pinion gears are driven. The pinion gears drive the two side gears, which in turn drive the axle (or half shafts) attached thereto.
The pinion shafts of the differential are supported by the differential housing so that the torque of the housing can be transmitted to the pinion shafts and thereby drive the pinion gears. The pinion gears spin upon the pinion shafts and rotate about the axis of the housing. A conventional differential housing utilizes either holes or slots in the wall of the differential housing to support the pinion shafts.
Pinion slots in the differential housing are shown in U.S. Pat. No. 6,743,138 issued to Visteon Global Technologies, Inc., hereby expressly incorporated by reference herein. As shown in FIGS. 3, 4, and 6, these slots assist in the assembly of the differential by permitting the axial loading of the pinion and gear set (e.g. spider-type pinion set). Specifically, FIG. 3 illustrates a differential housing 2 having slots 4 for axially loading a pinion shaft 6 having pinion gears 8. For example, the pinion gears 8 are secured to the pinion shaft 6 prior to axially inserting the pinion assembly into the housing 2. A cover 11 secures to the housing 2 to complete the assembly. FIG. 4 illustrates a spider pinion shaft 12 having four pinion gears 8 attached thereto. The spider pinion shaft 12 is axially inserted into the housing 2 by sliding within four slots 4 in the housing 2.
Another known differential assembly utilizes holes 20 in the differential housing 2 as shown in FIGS. 1, 2, and 5. The holes 20 permit a pinion shaft 22a to be inserted radially through the housing 2 from the exterior during assembly and supported therein during operation by locking pins mounted through the pinion shaft 22a and into the housing 2. The holes 20 support the pinion shaft 22a-22c such that the pinion gears 8 meshingly engage side gears 19. The pinion gears 8 may, for example, be positioned within the housing 2, and the pinion shaft 22a may be inserted from the outside of the housing 2 through each of the pinions gears 8.
Specifically, FIG. 2 illustrates four holes 20 in the housing 2 for insertion of the three pinion shafts 22a-22c. One of the pinion shafts 22a is capable of being inserted through one of the holes 20 from outside the housing 2. After insertion of the long pinion shaft 22a, the other pinion shafts 22b, 22c may be inserted through the holes in the housing 2. However, the hole-type design requires locking pins 25 for securing the shafts 22a-22c to the housing 2.
In addition, the hole-type design requires insertion of the pinion gears 8 into the housing 2 and feeding the shafts 22a-22c through the pinion gears 8. Therefore, with the hole-type feature, the pinion shafts 22 are separate parts that are inserted into the support holes 20 from the outside of the housing 2 during the assembly process requiring the coordination of numerous separate parts and assembly steps.
A spider pinion shaft 12 or a pinion shaft 6 having the pinion gears 8 attached thereto cannot be used with the differential housing 2 having the holes 20. The spider pinion shaft 12 requires the slots 4 for sliding the spider pinion shaft 12 into the housing 2. However, manufacturing the slot 4 is more expensive and requires special-purpose machines, like broach machines or coining machines, to process the slot 4 in an accurate circumferential position while maintaining an accurate width. Incorrect circumferential positioning of the pinion shafts 12 can cause extra damage load to the gear contact surfaces. Accurate slot width is necessary to ensure that the pinion shaft 12 can slide axially in the slots 4 without deflecting too far circumferentially. Too much circumferential deflection is detrimental to the contact surfaces of the pinion gears 8 and the pinion shaft 12.
Moreover, each of these known differential assemblies fails to provide adequate lubrication to the pinion gears 8 and the interior of the housing 2. In the hole-type embodiment, lubrication is limited from flowing through the housing 2 via the holes 20 due to the snug fit of the shafts 22a-22c in the holes 20. On the other hand, the slot-type design fails to provide any apertures in the housing for lubrication.
Accordingly, there is a need in the art for a differential housing capable of supporting axially loading pinion shafts, such as a spider pinion shafts, as well as supporting pinion shafts inserted from the outside of the housing, if desired. In addition, there is a need in the industry for a housing capable of using slots and holes to provide adequate lubrication to the pinion gears while maintaining the structural integrity of the housing. Moreover, there is a need to provide a housing capable of supporting pinion shafts without the use of locking pins while providing adequate lubrication into the housing.